The Expiatory Church of the Sagrada Familia is Gaudi's undoubted masterpiece. It charts the styles the architect evolved during his career. At the crypt level a Gothic design is used, but as the building climbs towards the sky the structure passes through the Art Nouveau stage before becoming more surreal and fanciful, climaxing in its intricately carved and ceramic encrusted spires. For all its apparent fantasy, however, the Sagrada Familia is rooted in sound structural principles, based on the parabolic arch and Gaudi's elaborate personal symbolism. Unfinished upon the architect's accidental death in 1926, the church is currently being completed following Gaudi's plans.